The packaging industry, food packaging particularly and more specifically the meat packing industry, has greatly benefited and advanced by the development and use of vacuum packaging techniques. The extraction of air from bagged meat product articles, for example, is a recognized and practiced prerequisite to the heat shrinking of heat shrinkable plastic packaging bags used in modern day poultry packaging and in "boxed beef" techniques, where primal cuts of meat, up to about forty or so pounds, random in size and shape, are bagged, evacuated, clip closed, and the bag heat shrunk to produce a packaged meat article which is easily handled for shipment, storage and ultimate use, with only less than freezing refrigeration conditions required rather than freezing for the preservation of the product.
The major criteria for effective vacuumizing of plastic bagged articles are that all possible air in the bag, with the article in place therein, including entrained air in crevices, folds and interstices in the meat article itself, be removed from the bag, that closure of the bag be effected while the bag interior is in its optimum vacuumized condition, and that the closure be complete, and continually made sequentially on bags of varying and assorted sizes in process, without damaging the bags structural integrity.
Other criteria include reliability of the apparatus, consistent reproducibility of results, ease of maintenance, cleanliness, ease of operation, and production speed capability.
Towards the attainment of these criteria and objectives, one of the vacuumizing systems developed and used involves first vacuumizing a closed zone in which a bagged article is disposed and then subsequently vacuumizing the bag itself independently. Typical apparatus for vacuumizing systems used in packaging articles in flexible bags according to this technique is described in U.S. Pat. No. 3,714,754 to Holcombe et al and U.S. Pat. No. 3,832,824 to Burrell, the descriptive teachings of which are incorporated herein by reference.
The vacuumizing packaging technique described in the aforesaid U.S. patent references comprehends an apparatus arrangement which includes a power driven belt conveyor, a vacuum hood, a vacuum source, clip closure means, motive means to actuate the conveyor, hood, and clip closure means, and operating and control components controllably interconnecting these elements. In operation, articles to be packaged are placed in open-mouthed plastic film packaging bags which are in turn placed on the conveyor, advantageously in an oriented manner through the use of jigs or product guides on the conveyor at regular spaced intervals. The articles on the conveyor are moved until one or more of them are located beneath the vacuum hood, at which time, the conveyor is stopped, the vacuum hood is lowered into sealing seating contact with the conveyor, the zone formed by the hood and the conveyor is evacuated, the bag interior is evacuated, the clip closure is applied while the bag interior is held at maximum vacuumized condition, vacuum is released, the hood raised and the bagged clip-closed article or articles moved from under the hood while the next item in sequence is simultaneously conveyed thereunder.
Alternatively, and as illustrated in the '824 patent, a short conveyor belt system may be contained completely within a vacuum chamber disposed between input and output conveyor elements. In this arrangement the seating seal is formed between the vacuum chamber hood which, when lowered, impinges on the chamber lower or body portion which completely contains the bagged article in place therein.
The two stage vacuumizing technique requires means to access the bag interiors to a vacuum connection. In the '754 patent this is accomplished by neck-gathering the open mouth of the bag around an extractor conduit and holding the necked-down bag folds in place thereon with scissor-like clamping elements. In the '824 patent, bag interior vacuumizing is accomplished by means of a second chamber within the vacuum chamber, separated from the main chamber by a wall. The bagged article resides in the main chamber while the mouth portion of the bag is gathered and held in necked-down pleated but unsealed condition.
In all of the known vacuumizing packaging techniques to which the present invention has applicability, the final closure of the bag in process is effected by a clipping device which crimps closed a metal clip tightly around the necked-down gathered folds of the bag material at the bag mouth. The clip closing mechanism is disposed at or adjacent the point where the bag material is gathered and held in its aforedescribed condition, and comprehends a magazine type supply source of clips arranged for one at a time dispensing and use, a clip drive attached to a hydraulically actuated rod connected to a hydraulic piston, hydraulic piston cylinder means, a clip crimping anvil juxtaposed to the clip drive, and hydraulic actuating means controllably connected to the control system of the vacuumizing equipment and arranged to drive and crimp close a clip around the gathered bag material upon completion of a preselected time of bag evacuation. Alternatively, the clip closing mechanism may be pneumatically actuated rather than hydraulically actuated.
In either case the clip closure action is initiated in each cycle when the vacuum level inside the bag in process reaches a preselected level and this, in turn, is governed by a time period in the control arrangement selected according to the size bag being evacuated. The evacuation period is known in the industry as the "soak time" and varies with bag size, longer soak times being required to effectively vacuumize larger bags, and shorter soak times for smaller bags.